CN1134090C - All-solid-state red and blue dual-color laser using superlattice as frequency conversion crystal - Google Patents

Abstract

The present invention relates to a fully solid bichromatic (red and blue) laser device using a super lattice as a frequency changing crystal. A laser device with bichromatic (red and blue) conversion outside a cavity, which is composed of a periodic optical super lattice, uses a semiconductor laser device as a pumping light source; a front surface which is mixed with a Nd: YVO4 crystal (3) is coated with a film to form a resonant cavity for lasers of 1.342 mum with a cavity mirror, and then, a LiTaO3 super lattice (8) whose period is 14.778 mum is arranged in a temperature controlling furnace (9) of a pumping light path. A red color, a green color and a blue color are three basic colors; a red laser device, a green laser device and a blue laser device have important application prospects in optoelectronic industry, such as high-brightness laser display, color printing, etc.

Description

All-solid-state red and blue dual-color laser using superlattice as frequency conversion crystal

1. Field of invention

The invention relates to a device for realizing short-wavelength laser output by using a superlattice to perform frequency doubling and triple frequency doubling. Especially all-solid-state red and blue dual-color lasers using superlattices such as lithium tantalate as frequency conversion crystals.

2. Background technology

Frequency doubling and triple frequency doubling by superlattice is an important means to realize short-wavelength laser output, which has always been paid attention to by people. The use of second-order nonlinear effects to achieve triple frequency must include two parameter processes of frequency doubling and sum frequency. Prior to this, related research work includes:

Zhu Shining and others published an article in Science in 1997 on realizing the triple frequency of green light by using quasi-periodic Fibonacci optical superlattice (QPOS), using the two reciprocal lattice vectors of the LiTaO ₃ superlattice of the quasi-periodic Fibonacci sequence to compensate The phase mismatch of the 1570nm fundamental wave in the two parameters of frequency doubling and summing produces effective 523nm triple frequency green light. The basic parameters of the superlattice are positive domain l=10.7 μm, two structural units A=24 μm, B=17.5 μm. The total length of the sample is gmm and the thickness is 0.5mm. The green light power generated by a single pass of 1570nm infrared light reaches 6mW, and the conversion efficiency is 23%.

Liu Zhaowei and others published an article titled "Double-period LT crystal triples the frequency of 1.064μm laser to generate ultraviolet laser" at the ISFD-6 conference in June 2000, reporting that the use of a double-period structure to realize the fundamental wavelength of 1.064μm The direct three times of the frequency, the two periods are l=6.77μm, L=51.08μm, and the designed matching temperature is 40°C. The highest conversion efficiencies of frequency doubling and triple frequency are 33% and 0.54% respectively.

M.Pierrou et al. published the article "Produce 740mW output blue light by intracavity frequency doubling with first-order level-matched KTP crystals" on Opt.Lett in 1999. The period of the KTP crystal used is 6.09 μm, the wavelength of the obtained blue light is 473 nm, and the conversion efficiency is 5.7%.

In the first article, the standard Fibonacci quasi-periodic optical superlattice was used to realize the direct output of tripled frequency green light at 523nm; the second article used a double-period superlattice to realize the tripled frequency of ultraviolet light at 355nm Direct output; the third article uses a periodic superlattice to achieve frequency-multiplied Blu-ray output. None of the above schemes involves the use of periodic superlattices to achieve 1.342 μm frequency doubling and direct frequency tripling at the same time.

3. Contents of the invention

The purpose of the present invention is: utilize periodic superlattice to realize simultaneously the frequency doubling of 1.342 μ m laser and the direct triple frequency output, utilize Nd-doped crystal such as Nd:YVO4 The property of excellent laser crystal, and according to design have specific period LiTaO ₃ ferroelectric domain superlattice, the superlattice can achieve efficient frequency doubling and triple frequency at the same time for the 1.342μm emission of Nd:YVO4 crystal, so as to construct a small all-solid-state laser that can realize red and blue two-color laser output .

The purpose of the present invention is achieved in the following manner: an all-solid-state red and blue dual-color laser with a superlattice of materials such as lithium tantalate as a frequency conversion crystal is characterized in that it is an extracavity red and blue two-color laser composed of a periodic optical superlattice The converted laser consists of a semiconductor laser as the pumping light source, the front surface coating of the Nd:YVO ₄ crystal (3) and the cavity mirror (5) together form a _1.342 μm laser resonant cavity; The superlattice (8) is placed in the temperature-controlled furnace (9) of the pump light path, and the wavelength of the fundamental wave laser is 1.342 μm. The present invention can choose different Nd-doped laser crystals, adopt the excitation line of ⁴ F _3/2 -> ⁴ I _13/2 , and design LiTaO ₃ superlattices of different periods according to the emission wavelengths corresponding to different crystals.

1. The emission of Nd:YVO ₄ crystal with a wavelength of 1.342μm is just within this range, the corresponding matching temperature is 74.1℃, and the corresponding period is 14.778μm. From the above analysis, it can be seen that the wavelengths of several nanometers around 1.342 μm can be frequency-doubled and tripled by the periodic LiTaO ₃ superlattice (see attached figure), because ^{the 4} F _3/2 - > ⁴ I _13/2 The emission line has a small shift relative to 1.342μm, which means that other Nd-doped laser crystals can also use this periodic LiTaO ₃ superlattice to generate frequency-doubled red light and tripled blue light Nd:YVO ₄ Only the corresponding fundamental wavelength, matching temperature and superlattice period are slightly different. This design scheme is also applicable to other nonlinear crystals, such as LiNbO ₃ .

2. The present invention is applicable to the optical superlattice to perform frequency doubling and tripling on the emission of ⁴ F _3/2 -> ⁴ I _13/2 corresponding to all laser crystals containing Nd ions, and simultaneously obtain two laser beams of red and blue . For example, Nd:YAG crystal and Nd:YAP crystal, the emission wavelengths of their corresponding spectral lines are 1.325μm and 1.341μm respectively, and they can use this superlattice material to obtain red light at 663nm, blue light at 442nm and red light at 671nm respectively. Light with 447nm blue light.

In addition to the periodic superlattice, the present invention also includes all other quasi-periodic, double-periodic and other series of non-periodic optical superlattices to double and triple the frequency of the above-mentioned laser light, and simultaneously obtain two beams of red and blue laser light. For example, LiNbO ₃ crystal can be used, and the quasi-periodic superlattice can also be used to achieve frequency doubling and triple frequency for this spectral line of Nd. Corresponding to the Nd:YVO ₃ crystal, the quasi-periodic structural parameters are D=15.329μm, D _A =16.300μm, D _B =12.493μm, positive domain width Lc=6.2μm, and the parameter τ=0.17395 related to the projection angle, corresponding to The matching temperature is 120°C. The selection condition of the quasi-periodic parameter is to make the reciprocal lattice vector in the reciprocal space meet the quasi-phase matching condition in the coupling optical parameter process: and it is a two-component periodic structure, and the two-component quasi-periodic structure is composed of two primitives A and B Arranged in a quasi-periodic sequence, the sequence can be obtained by the method of projection. That is, make a straight line with a slope of tanθ in a two-dimensional square lattice, and the width of the projection area is sinθ+cosθ. The projection points of the grid points in the area to the straight line constitute a quasi-periodic sequence of two components with a projection angle of θ. The quasi-periodic dielectric superlattice material of the present invention is a material with a microstructure prepared by the above-mentioned setting method, and LT and LN lattice materials are typical. For example, see 0019006.7 and 0019007.5 of the applicant for the arrangement and preparation method of dielectric superlattice materials with periodic and quasi-periodic structures.

3. In addition to LiTaO ₃ crystals, the present invention also includes optical superlattices of LiNbO ₃ , KTP, RTP and other nonlinear optical crystals. According to the refractive index dispersion relationship of these crystals, the laser wavelength corresponding to the above-mentioned laser crystals can be designed The optical superlattice with a specific structure and structural parameters realizes the frequency doubling and tripling of the laser, and simultaneously obtains the red and blue laser beams.

Periodic optical superlattices are usually only used for frequency conversion of single parametric processes such as frequency doubling, sum frequency or difference frequency. The reciprocal lattice vector of a periodic superlattice can be expressed as $G=\mathrm{<figure-callout\; id="2"\; label="m"\; filenames="C0110802400091.png"\; state="\{\{state\}\}">m</figure-callout>}\frac{2\mathrm{\&pi;}}{\mathrm{\&Lambda;}},$ Among them, Λ is a period, m is an integer, that is, all reciprocal lattice vectors are integer multiples of the first-order reciprocal lattice vectors. Generally, only one of the reciprocal lattice vectors of the periodic structure can compensate the phase mismatch of a single parametric process under the incident condition of a single frequency fundamental wave. In the normal dispersion region of the material, each crystal can only use two different reciprocal lattice vectors to compensate the double frequency of the fundamental wave and the sum frequency of the fundamental wave and the second harmonic in a narrow range of more than ten nanometers near a certain characteristic wavelength. The phase mismatch of the two parametric processes makes the two parametric processes coupled to each other, directly realizes the frequency triple, and obtains part of the output of the remaining frequency doubled light at the same time.

The design idea of the structure is as follows:

The width ratio of the positive and negative electric domains of the periodic structure is 1:1, and only the reciprocal lattice vectors of odd orders are taken due to the extinction of even order reciprocal lattice vectors. The phase mismatch of the multiplier is smaller than that of the sum frequency. In order to utilize the maximum effective nonlinear coefficient, the phase mismatch of the multiplier is compensated by the first-order reciprocal lattice vector of the periodic structure, namely $\frac{2\mathrm{\&pi;}}{\mathrm{\&lambda;}}(2{\mathrm{no}}_2-{2\mathrm{no}}_1)-\frac{2\mathrm{\&pi;}}{\mathrm{\&Lambda;}}=0---\left(1\right)$

λ is the fundamental wavelength, and Λ is the period. n ₁ and n ₂ are the refractive indices of the fundamental wave light and the frequency doubled light, respectively. The reciprocal vector of compensation and frequency-phase mismatch takes the third order, namely $\frac{2\mathrm{\&pi;}}{\mathrm{\&lambda;}}(3{\mathrm{no}}_3-{2\mathrm{no}}_2-{\mathrm{no}}_1)-3\frac{2\mathrm{\&pi;}}{\mathrm{\&Lambda;}}=0---\left(2\right)$

From equations (1) and (2) we get

3(2n ₂ -2n ₁ )＝3n ₃ -2n ₂ -n ₁ …………(3)

We use the following dispersion formula to calculate the refractive index ${{\mathrm{no}}_e}^2(\mathrm{\&lambda;},T)=A+\frac{B+b\left(T\right)}{{\mathrm{\&lambda;}}^2-[C+c\left(T\right){]}^2}+\frac{\mathrm{E.}}{{\mathrm{\&lambda;}}^2-{\mathrm{<figure-callout\; id="2"\; label="f"\; filenames="C0110802400091.png"\; state="\{\{state\}\}">f</figure-callout>}}^2}+{\mathrm{D\&lambda;}}^2$

The parameters are:

A=4.5284, B=7.2449×10 ^-3 ,

C=0.2453, D=-2.3670×10 ^-2 ,

E=7.7690×10 ^-2 , F=0.1838,

b(T)=2.6794×10 ^-8 (T+273.15) ² ,

c(T)＝1.6234×10 ^-8 (T+273.15) ² .

There are two unknown parameters λ and T in the above equation, λ is the wavelength of the fundamental light, and T is the temperature. Because it is easier to realize the matching temperature between 0°C and 150°C in practice, the corresponding fundamental light wavelength calculated according to formulas (1), (2), and (3) is 1.336 μm to 1.349 μm (as shown in Figure 2) . The emission of Nd:YVO ₄ crystal with a wavelength of 1.342 μm is just within this range, the corresponding matching temperature is 74.1°C, and the corresponding period is 14.778 μm. From the above analysis, it can be seen that the wavelengths of several nanometers near 1.342 μm can be frequency-doubled and tripled by the periodic LiTaO ₃ superlattice, because the corresponding ⁴ F _3/2 -> ⁴ I ₁₃ of Nd ions in different crystals _{The /2} emission line has a small shift relative to 1.342 μm, which means that other Nd-doped laser crystals can also use this periodic LiTaO ₃ superlattice to produce frequency-doubled red light and tripled blue light, but the corresponding fundamental wavelength, There are slight differences in matching temperature and superlattice period. This design scheme is also applicable to other nonlinear crystals, such as LiNbO ₃ . Only because the corresponding refractive index formulas are different, the wavelength ranges that can satisfy the phase matching conditions are also different.

Advantages of the present invention:

1. Red, green, and blue are three basic colors. Red, green, and blue lasers have important application prospects in optoelectronic industries such as high-brightness laser display and color printing. At present, among the three-color lasers, only the green laser technology is relatively mature and has become a commodity, while the red and blue lasers are still in the stage of technological exploration. The invention can generate red and blue two-color lasers from one laser device, so it has extremely high application value.

2. The optical superlattice with other structures can also double and triple the frequency of the laser near 1.342 μm to achieve simultaneous output of red light and blue light. The present invention adopts the optical superlattice of periodic structure, and its superiority lies in that the effective nonlinear coefficient of periodic structure is higher than other complex structures such as quasi-periodic, double-periodic, non-periodic, so it is easier to obtain higher frequency doubling, triple frequency output.

3. The simple periodic structure is more convenient and easy to control than the complex structure in the design, plate making, photolithography and polarization preparation process.

4. The Nd:YVO ₄ crystal has the advantages of large absorption coefficient, wide absorption bandwidth, large emission loading area, and linearly polarized output. In this crystal, the Nd ion ⁴ F _3/2 -> ⁴ I _13/2 corresponding to 1.342 μm emission The energy level transition has relatively strong relative intensity, so a higher power laser output of this wavelength can be obtained under a lower threshold condition. The 1.342μm laser suitable for LiTaO ₃ crystal is the four-level structure of Nd:YVO ₄ crystal, which has a large absorption cross section and high light-to-light conversion efficiency, so it is easy to generate high fundamental wave output and obtain high Multiplier and tripler output.

4. Description of drawings

Below in conjunction with accompanying drawing and concrete experimental example the present invention is described in further detail:

Fig. 1 is a schematic diagram of a laser that simultaneously outputs quasi-continuous red light and blue light using the present invention.

Figure 2 is a diagram of the matching relationship between the triple frequency triplet of periodic lithium tantalate superlattice blue light, and the LiTaO ₃ superlattice with a period of 14.778 μm corresponds to the fundamental wavelength of the double frequency red light and triple blue light. The temperature, the abscissa and the ordinate are the matching temperature wavelength and the corresponding cycle respectively.

Fig. 3 is a structural schematic diagram of a coating design of a laser that simultaneously outputs quasi-continuous red light and blue light using the present invention.

Figure 1 is as follows:

(1)-semiconductor laser (LD) with a wavelength of 809nm;

(2)-focusing system, generally a lens group;

(3) -Nd:YVO ₄ crystal, laser medium for producing 1.342μm laser;

(4)-Q-switching device (such as acousto-optic device);

(5) Output mirror of -1342nm laser (such as T=8%);

(6)-converging lens (such as f=25mm);

(7) - temperature control furnace, used to tune the temperature;

(8)-Periodic superlattice crystals, which produce frequency-doubled red light and triple-frequency blue light;

(9) - output red and blue two-color laser;

(10) - Anti-reflection coating of multilayer film 1342nm, high reflection coating of 671nm;

(11)-Multilayer film, 671nm high reflection film, 447nm high transmission film

5. Specific implementation

Example 1

Make an extracavity red-blue two-color conversion laser composed of a periodic optical superlattice according to Fig. 1 (this process has been realized experimentally). The model of the LD is OPC-DO15-809, the output wavelength is 809nm, and the maximum output power is 15W. The front surface of the Nd:YVO ₄ crystal (3) is coated, and the cavity mirror (5) together constitutes a resonant cavity of 1.342μm laser. Through the acousto-optic switch, a quasi-continuous 1.342μm laser with an average power of about 500mW can be generated behind the cavity mirror (5), the repetition frequency is 10KHz, and the pulse width is about 30ns. A prepared piece of LiTaO ₃ superlattice (8) with a period of 14.778 μm (1.8 cm in length) is placed in a temperature-controlled furnace (7). Adjust the temperature of the temperature-controlled furnace. At the matching temperature, the output of red light and blue light reaches the maximum, and the conversion efficiencies are 41.9% and 10.3%, respectively.

Example 2

According to Figure 2, a red and blue laser composed of periodic superlattice is fabricated. The difference from Example 1 is that the front and back surfaces of the superlattice are respectively coated with multi-layer films. The front surface is coated with 1.342μm antireflection coating and 671nm high reflection coating; the back surface is coated with 671nm high reflection coating and 447nm high transmission coating. In this way, the 671nm red light obtained by frequency doubling is resonated inside the superlattice to increase its intensity, which can increase the conversion efficiency of triple frequency blue light. At the same time, changing the transmittance of the back surface to 671nm can change the ratio of red light and blue light output.

Claims (3)

1. An all-solid-state red and blue two-color laser with a superlattice as a frequency conversion crystal, which is characterized by an extracavity red and blue two-color conversion laser composed of a periodic optical superlattice. A semiconductor laser is used as a pumping light source. The crystal (3) and the cavity mirror (5) doped with Nd: YVO ₄ front surface coating form the resonant cavity of the 1.342 μm laser; then a LiTaO ₃ superlattice (8) with a period of 14.778 μm is placed in the control of the pumping optical path In the warm furnace (7). 2. The all-solid-state red and blue two-color laser with superlattice as frequency conversion crystal according to claim 1, characterized by periodic, quasi-periodic, non-periodic or serial periodic structure, including lithium tantalate, lithium niobate or The KTP superlattice material is a frequency-converting crystal, with Nd:YAG, Nd:YAP Nd-doped crystal as the laser medium, excited by the transition of Nd ions ⁴ F _3/2 -> ⁴ I _13/2 at 1.3μm--1.4μm The wavelength between them is the fundamental wave, and all solid-state blue lasers are pumped by all semiconductor lasers that achieve blue light triple frequency by quasi-phase matching. 3. The all-solid-state red and blue two-color laser with superlattice as frequency conversion crystal according to claim 1, characterized in that said optical superlattice crystal is Nd ion ⁴ F _3/2 -> ⁴ I _13/ The wavelength between 1.3 μm and 1.4 μm excited by _{the 2} transition is the fundamental wave, and all solid-state blue lasers pumped by all semiconductor lasers that achieve blue light triple frequency by quasi-phase matching.

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